Cineversity

Any idea how to fix edges when using matte objects. Obviously the problem is from the anti-aliasing, but how this is still a thing?!?

I tried method with simple choker like one of Tim Clapham videos:
https://www.youtube.com/watch?v=lcc1U-0ejCg

But in my case when I have more things to cut out this technique just messes my compositing? Any idea how to render it so this wouldn’t happen?
Scene and exr renders:
http://we.tl/WyFgNEofh0

Hi Nikolay,

Would you mind uploading the scene to the link I have send you via PM.

Your upload service: Sorry, I have no time to read seven(!) pdfs, to know what I agree to, and to just press the agree button without really knowing what I agree to seems pretty (…) careless to me.

Thanks a lot.

I advice against altering any matte/mask/alpha, as long it is not clear where the problem came from. Your post indicates that we agree here. Yes, I saw people suggesting it, but without knowing the source of the problem, well, how much value has such a general idea? Sometimes that makes perhaps sense, but it limits the quality of the mask in most cases. Again, I’m not arguing here against anyone, as I haven’t seen the tutorial.

If it is Anti-Alias [AA] based, then you need to render properly, I think that is pretty safe to say. I have to see it of course, to know if it is at all an AA problem.

I will check your content when i get it.

In any case, I highly suggest to render out each object on its own, if possible with straight-alpha and avoid non 3d objects in the scene, e.g. the Background Object.
Any pixel touching mask values below 1.0 (100% white) should have fully ownership of the color value when masked, hence straight alpha is the preferred method for pristine color correction/finishing. A pixel value that is AA’d (i.e., mixed with something else) can’t be separated with a mask anymore. If any stronger color correction is applied, the “edge” will show up, if the two objects had, e.g., complementary colors. Similar to that, premultiplied problems, where transparent RGB values become masked again, etc..
Any of those, will normally disqualify the work, if the Finishing QA is tight.

Another typical point was over the years showed as a workflow problem with mixed linear and gamma based workflows.

All the best

Thanks for the file, Nikolay.

There was a plug-in in used that I do not have.

I couldn’t find any connection between the Object-Buffer 1 to 9, and the scene file. So I set them up to be 1 to 5

I have send you the link to the Ae comp file via Private Message (PM Cineversity).

You will find two examples and none has the little lines. Please use the Linearize* Workflow: You will see changes of the transparence parts, which are certainly noticeable. If you set up a complete Linear 32 bit/float/channel workflow, the Alpha channels will not change if set to preserve RGB [in Ae]. Which shouldn’t be needed to be set in the first place, as it doesn’t matter in Linear Workflow, but it is a good indicator if there is a flaw. Yes, there is a lot of nonsense on the web about.

*(I left the linearize off in Ae in the provide project file, as your project was set up as sRGB input, which makes a difference. Not my suggestion at all to work that way if 32bit/channel-float.)

I encourage you to see the advantage of Straight Alpha options, as it has much more quality for the final work. Especially for finishing, which is in advertisement certainly a key.

If you need to go the route with the initial set up, please feel free to contact the support as well.

All the best

[edited for clearness]

Images: the yellow stripes are “solids” that I used to explore the edges. Yellow here as the bottle were dark blue, change the color as well to red and green, to see everything possiible.

Did you rendered the bottles and the floor separately? Because I don’t see an object buffer used in Ae comp. Also the linear workflow is not turned on in Ae. I know that when ground and bottles are rendered separately, there is no problem, the problem comes when you render the whole scene and then try to cut out the bottles by object buffers so I can do color correction to each bottle.

Hi Nikolay,

I think we run in circles here. Everythink you ask is already answered and discussed. What else can I do. The impression that I get is, that my replies are not read by you.

I can try it again, if you mix pixels, e.g., dark and bright ones, then you get of course in the “seam” of the two a mix of the two, no Object Buffer has the option to ” un-mix” this.

You need to explore the difference of premultiplied and straight alpha. In the multipass series I have dedicated quite some time to get this difference across. It is an industry standard and straight is the better way, as mentioned above.

Let me know if there is something else

All the best

Hi,
most of the time is difficult for me to understand you, because English is not my first language :D I think I get the idea with the straight alpha. “I can try it again, if you mix pixels, e.g., dark and bright ones, then you get of course in the “seam” of the two a mix of the two, no Object Buffer has the option to ” un-mix” this.” - this I can’t really understand, I know what the words mean, but I miss the whole idea :D. Please send me a link of your multipass series.

Thanks!

Thanks for sharing, Nikolay.

I will try in a different way. Simplified!

A pixel value is like a formula, speaking of Object Edges:

(Object1 + Object2) / 2 = Pixel Value

Object1 = 12

Object2 = 188

(12+188)/2=100

This is Anti-Alias, if both objects have half of the pixel covered.

The “Object Buffer” for each has now a single gray value for “Object1—Object-Buffer1” and for “Object2—Object-Buffer2”

What ever the value is, it is the transparency of of a pixel with the value 100, not 12 not 188. A mix.

I have tried to translate it with Google, and translated it back as check, and I got the typical roughness:

Intro

http://www.cineversity.com/vidplaytut/multi-pass_in_depth_003_alphamaskmatte

Straight vs Premultiplied

http://www.cineversity.com/vidplaylist/sassis_tooltime_tips_multi-pass_rendering/multi-pass_in_depth_005_straight_pre-multiplied_alpha

Of course there is always the manual:
https://help.maxon.net/#DRENDERSETTINGS-RDATA_GROUP_SAVE

Scroll down.

Thanks a lot! English is best option :D and I’m from Bulgaria we speak bulgarian. Thank you, you are so kind!

Ha! My bad, I have fixed it, it is now in Bulgarian.

I’m really sorry, I have to use a different IP checker in the future!

Are you in mathematics, or more into visuals, perhaps into something else, I ask—so I can adapt my examples?

I really like you to have that information as clear as possible, as it will improve your decisions about quality and time investment for any project.

All the best

Mostly I’m visual guy, and mathematics is not for me :D. I got the idea for the alpha channels with one recent video from the foundry, but I was confused about straight alpha, but it turned out its just unpremultiplied alpha. Here is the video:
https://www.youtube.com/watch?v=glnluXLg9KU

I was also confused about object buffers - why they exist if its better to render the objects separately. Or the straight alpha will fix also the problem with the buffers? If I render full image - bottles and BG in one EXR and then in after pull out the BG and the bottles with Object buffers on separate layers, will this problem occur? And does I have to use the linear workflow chekbox in Ae?

Hi Nikolay,

Steve Wright is a great instructor, I followed him since I had as his “student” a hands-on class in 2005 in San Francisco with him (GreenScreen Intensive, 10 days).

What he said is correct, and pretty much all he says, especially in his many books. I have read all, and every edition. So, I guess I know what he is talking about ;o). Since you have the visuals from him, I can leave it that way.

What you take away from it, “… but it turned out its just unpremultiplied alpha. …”, is not in general true.I don’t know even how to understand it that way from his content. If the RGB values were mixed before with other values, not straight, then no un-premultiply option with a gray map based matte/alpha will cure this. Not possible—this is important to understand!

A premultiplied image must have the RGBA information stored, as RGB has by itself no transparency information. BUT the RGB can be straight or mixed (on the edges or in semi transparent areas). If it is based on a mixture, again, it will not turn at any time into a straight RGB value for that object just by un-multiply it.  It NEEDS (!) to be render separate and straight to be that way. No shortcut, no magical Nuke Node can do that. In his green-screen matte (later in the clip) you will not find the term “straight”, BTW.

Object Buffer, have no idea what they do in terms of Premultiplied or Straight. They just estimate the needed values to make the object transparent or semi transparent where it is given by the object. This is independent from Premultiplied or Straight, simply put, any alpha.

If the color values are very close of the Object1 and Object2 along the edge, then it works in any case to a certain degree and quality. Mostly this is used when time is of the essence or other reasons, missing knowledge.
The idea to “choke” the matte, would leave a black seam on your floor, or if done for both a gap in the compositing.

Often Buffers are rendered out for minor color corrections or in the same way to fade the colors of a back ground object, to simulate “atmosphere”. Those minor adjustments work great with a single pass RGB and Object Buffer.
But when it comes to heavy color corrections, the edge pixels are most-likely wrong after that. Again, it si about quality vs time.

In this Quality vs Time area, Cinema 4D has to deliver both options, as users request this. It doesn’t mean that when it is possible to do, that you get both, great quality and a short time (e.g., render)

(As a side note, if you follow NUKE and the idea of deep compositing, then we have to talk on a complete different level, since C4D has not that option, this forum is not the place for it.)

All the best

This is a screenshot from the tutorial, and clearly it is straight alpha image to begin with not mixture of any other object